Commitments and Contingencies - Additional Information (Detail)					1 Months Ended					6 Months Ended	12 Months Ended
	May 01, 2018 USD ($) ft²	Oct. 06, 2017 ft²	Apr. 07, 2017 USD ($) ft²	Sep. 21, 2016 ft²	Dec. 31, 2017 USD ($)	Feb. 28, 2017 USD ($)	Nov. 30, 2016 Term	Jul. 31, 2015 ft²	May 31, 2013 USD ($)	Jun. 30, 2018 USD ($)	Oct. 31, 2017 USD ($)	Sep. 30, 2015 ft²
Commitment And Contingencies [Line Items]
Operating lease term									42 months
Minimum monthly lease payments	$ 87,000								$ 17,588
GeneQuine Biotherapeutics GmbH (“GeneQuine”) [Member] | Definitive Agreement [Member]
Commitment And Contingencies [Line Items]
License agreement, upfront fee paid					$ 2,000,000
Future milestone payments owed										$ 0
GeneQuine Biotherapeutics GmbH (“GeneQuine”) [Member] | Definitive Agreement [Member] | Maximum [Member]
Commitment And Contingencies [Line Items]
Additional milestone payments					54,000,000
Evonik Corporation [Member]
Commitment And Contingencies [Line Items]
Supply agreement period							5 years
Supply agreement renewal term							2 years
Number of renewal terms | Term							2
Supply agreement description										The Supply Agreement will renew for two successive two year terms upon mutual written consent by both parties.
Manufacturing and Supply Agreement with Patheon UK Limited [Member]
Commitment And Contingencies [Line Items]
Manufacturing agreement period								10 years
Phase 2 Proof of Concept (PoC) Clinical Trial [Member] | GeneQuine Biotherapeutics GmbH (“GeneQuine”) [Member] | Definitive Agreement [Member] | Maximum [Member]
Commitment And Contingencies [Line Items]
Additional milestone payments					$ 8,700,000
Burlington Massachusetts [Member]
Commitment And Contingencies [Line Items]
Additional leased office space | ft²		6,450	1,471					4,700
Extended leased office space | ft²								5,400				5,400
Office space leased on temporary agreement | ft²				6,700				6,700
Lease termination date	Oct. 31, 2023		Oct. 31, 2023					Oct. 31, 2019
Temporary lease termination date				Oct. 31, 2017
Office space leased | ft²			28,600
Lease payment per month for office space											$ 80,000
Lease payment per month for additional office space			$ 4,100
Operating lease office space | ft²	36,500
Operating lease commencement date		2018-04
Woburn, Massachusetts [Member]
Commitment And Contingencies [Line Items]
Operating lease term						5 years
Monthly lease payment						$ 15,000
Total cash obligations for lease						$ 900,000